1. Field of the Invention
The present invention relates to a toroidal continuous variable transmission adapted for the vehicle such automobiles.
2. Description of the Prior Art
In most toroidal continuous variable transmissions conventionally used incorporated in the transmission systems in automotive vehicles, the input and output shafts are arranged in a single row along the common centerline. To cope with many restrictions on the layout of the transmission systems, a countershaft having a gear meshed with an output gear connected to an output disk is arranged parallel to an input shaft astride the toroidal transmission mechanism while a spur gear mechanism is arranged-between the countershaft and the output shaft. For getting the rotation of the output disk to the output shaft, thus, either engaging or disengaging a clutch incorporated in the automotive power train brings the output shaft any one of the forward, reverse and neutral. Nevertheless, this prior construction raises major problems of rendering the continuous variable transmission too bulky in its diameter to mount efficiently the transmission to the automotive vehicle.
Among continuous variable transmissions having toroidal continuous variable transmission mechanisms is known a continuous variable transmission, as shown in FIG. 3, in which the input and output shafts are arranged in a single row on the common centerline and the rotation of the input shaft may be transmitted to the output shaft with forward speeds, neutral and reverse by speed-changing operation of the toroidal transmission mechanism without no provision of the countershaft so that the continuous variable transmission is reduced in the diametric dimension. Refer to, for example, the disclosure in U.S. Pat. No. 5,607,372.
The continuous variable transmission shown in FIG. 3 is a continuous variable transmission including therein a toroidal continuous variable transmission mechanism of double cavity type. The toroidal continuous variable transmission mechanism is comprised of a first toroidal transmission unit 8 and a second toroidal transmission unit 9, which are arranged on an input shaft 1 in opposition to each other. The first toroidal transmission unit 8 includes a first input disk 2, a first output disk 3 arranged confronting the first input disk 2, and pivoting power rollers 6 to transmit torque from the first input disk 2 to the first output disk 3, while the second toroidal transmission 9 has a second input disk 4, a second output disk 5 arranged confronting the second input disk 4, and pivoting power rollers 7 to transmit torque from the second input disk 4 to the second output disk 5. The power rollers 6, 7 are each for rotation on its own rotating axis 11 and also supported by a trunnion, not shown, for pivoting motion about its associated pivotal axis 12 that is normal to the rotating axis 11 and normal to the plane surface of this paper. This makes it possible to pivot the power rollers 6, 7 in cooperation with each other whereby the speed ratio may be varied infinitely in accordance with pivoting angles of the power rollers 6, 7 about the pivotal axes 12.
While the torque transmission between any paired confronting input and output disks 2, 4 and 3, 5 through the power rollers 6, 7 depends on a shearing force or traction (viscous-frictional force) of hydraulic fluid, the desired tractive effort should require much contact force acting along the axis of the transmission at areas where the power rollers 6, 7 come in rolling-contact with the input and output disks 2, 4 and 6, 7. To cope with this, the prior toroidal transmission mechanism is commonly provided with a loading cam 10, or means for adjusting a contact pressure of the power rollers 6, 7 against the disks, depending on the magnitude of the torque that is applied to the input disks 2, 4 from the input shaft 1. In the prior transmission illustrated, a pair of output disks 3, 5 are made integrally with one another. Reference letters A and B in the accompanying drawing denotes rotational directions of the input and output shafts, respectively. The input shaft 1 extends to the output end, passing through the input and output disks 2, 4 and 3, 5 of the toroidal transmission mechanisms 8, 9. A hollow drive shaft 15 integral with the output disks 3, 5 fits over the input shaft 1 for free rotation and also supports thereon the second input disk 4 for rotation.
The torque applied to the input shaft 1 from the engine is transmitted to the first input disk 2 through the loading cam 10 and, at the same time, transmitted to the second input disk 4 past the input shaft 1. Rotation of the first input disk 2 by the transmitted torque causes the first power rollers 6 rotate so as to turn the first output disk 3. On the other hand, the torque transmitted to the second input disk 4 drives the second output disk 5 through the second power rollers 7. It will be understood that the first and second output disks 3, 5 are made in an integral structure to rotate together in unison. When the power rollers 6, 7 are pivoted about their pivotal axes for a desired angle in synchronized relation with one another in the event during which the torque is transmitted, the rolling-contact locations of the power rollers 6, 7 with the input and output disks 2, 4 and 3, 5 moves infinitely, thereby resulting in making the transmission ratio vary in a continuous manner.
Arranged downstream of the second toroidal transmission unit 9 is a drive mechanism 46 that is in coaxial relation with both of the input shaft 1 and hollow drive shaft 15 and establishes a power train between the input shaft 1 and the hollow shaft 15. The drive mechanism 46 is comprised of a first sun gear 47 integral with the input shaft 1, a carrier 48 mounted on the input shaft 1 and also connected integrally with the second input disk 4, a torque tube 52 supported for rotation on an extension 14 of the input shaft 1, a second sun gear 53 provided on the torque tube 52 at the upstream end thereof, and a pinion 49 commonly referred as step-gear. The pinion 49 is supported for rotation at a middle journal thereof and has a gear 50 meshed with the first sun gear 47 and another gear 51 meshed with the second sun gear 53, the gears 50 and 53 being arranged on axially opposite ends of the middle journal, one to each end. With the construction as described just above, as the first sun gear 47 is opposite in rotating direction to the carrier 48, the pinion 49 revolves around the first sun gear 47, spinning on its own axis, to thereby rotate the torque tube 52 in the same rotating direction as the hollow drive shaft 15.
Rotation of the drive mechanism 46 is transmitted through the torque tube 52 to an output gearing mechanism 54 consisting of first and second planetary gearsets 55 and 56. The first planetary gearset 55 comprises a third sun gear 57 attached to the torque tube 52, a first pinion 58 supported for rotation on a mount member 60 fixed to a stationary case and meshing with the third sun gear 57, and a first ring gear 59 in mesh with the first pinion 58. The second planetary gearset 56 includes a fourth sun gear 61 attached to the torque tube 52, a second pinion 62 supported for rotation to a carrier 64, and a second ring gear 59 connected to the extension 14 of the input shaft 1 and meshing with the second pinion 62. The first ring gear 59 of the first planetary gearset 55 and the carrier 64 of the second planetary gearset 56 extend downstream so as to be selectively connected to the output shaft 40 via either a high-range clutch 65 or low-range clutch 66.
When engaging the high-range clutch 65 whereas disengaging the low-range clutch 66, the transmission ratio becomes the high-range operation. In contrast, when the low-range clutch 66 is engaged to select the low-range operation, the second ring gear 63 rotates in the same direction as the direction A of the input -shaft 1. The fourth sun gear 61, however, rotates in the opposite direction B, but at a speed varying depending on a magnitude of transmission ratio of the toroidal transmission units 8, 9. Although the output shaft 40 may is turned at a revolving speed of the second pinion 62, but shifted into any one of forward, neutral and reverse, depending on the rotating speed of the fourth sun gear 61, which varies in accordance with the speed-changing operation at the toroidal transmission units 8, 9. Moreover, the rotating speed of the fourth sun gear 61 affects the magnitude of rotating speed of the output shaft 40 at forward and reverse rotation. When the toroidal transmission units 8, 9 provide the transmission ratio of the maximum overdrive, the overall transmission comes in reverse. In contrast, when the toroidal transmission units 8, 9 provide the transmission ratio of the maximum reduction, the overall transmission comes in forward. Thus, any transmission ratio between the maximum overdrive and the maximum reduction may render the overall transmission neutral and no torque converter or clutch is necessary even under some conditions, as in starting a stationary vehicle. The transmission constructed as described above makes it possible to eliminate the countershaft arranged parallel to an input shaft astride the input disk, thereby resulting in reducing the overall diametric size of the transmission.
Nevertheless, the continuous variable transmission having the toroidal continuous variable transmission as described above needs the components: the step-gear for the pinion 49 revolving just as the planet in the drive mechanism 64, and first and second pinions 58, 62 in the first and second planetary gearsets 55, 56, respectively, in the output gearing mechanism 54. In addition, the drive mechanism 46 and output gearing mechanism 54 are arranged in series along the same axial direction. Thus, the prior continuous variable transmission has a major problem of becoming much longer in the overall length of the transmission. Taking into account the major problem that the in-line arrangement of the drive mechanism and the output gearing mechanism along the common centerline results in increasing the overall length of the transmission, it may be worthwhile considering incorporating or uniting any one of the planetary gearsets into the drive mechanism and arranging another planetary gearset downstream of the drive mechanism so as to arrange the planetary gearsets in two row, thereby providing selectively any one of forward motion, neutral and reverse in the overall transmission in accordance with the speed-changing operation at the toroidal transmission units, and further making it possible to reduce overall length of the transmission.